RIE process for fabricating submicron, silicon electromechanical structures

Abstract

A reactive ion etching process is used for the fabrication of submicron, single crystal silicon, movable mechanical structures and capacitive actuators. The reactive ion etching process gives excellent control of lateral dimensions while maintaining a large vertical depth in the formation of high aspect-ratio freely suspended single crystal silicon structures. The silicon etch process is independent of crystal orientation and produces controllable vertical profiles.

What is claimed is: 
     
       1. A reactive ion etching process for fabricating a high aspect ratio, submicron, released, single crystal silicon electromechanical structure independently of crystal orientation, comprising: forming a patterned etch mask on a top surface of a single crystal silicon substrate, the etch mask defining a structure of arbitrary shape to be formed in said substrate, said shape being independent of crystal orientation in said substrate;   transferring the pattern of said etch mask to said substrate and forming by reactive ion etching trenches defining the structure to be fabricated in the substrate, said etching step forming trenches having bottom walls and vertical side walls;   forming an electrically insulating silicon dioxide layer on exposed surfaces of said silicon substrate, the exposed surfaces including said vertical side walls of said trenches;   forming metal electrodes on selected portions of said vertical side walls;   selectively removing said silicon dioxide insulating layer from said bottom walls of said trenches to expose said single crystal silicon substrate; and   reactive ion etching the exposed bottom wall substrate to undercut and to mechanically release said defined structure from said substrate to thereby produce a high aspect ratio, released, single crystal silicon structure having vertical side walls, said released structure being relatively movable with respect to said substrate.   
     
     
       2. The process of claim 1, wherein the step of forming metal electrodes includes depositing on said silicon dioxide layer a conformal layer of metal; producing an electrode pattern on said layer of metal; and   selectively removing said deposited metal to produce said electrodes on at least selected portions of said vertical side walls.   
     
     
       3. The process of claim 2, wherein the step of forming a patterned etch mask includes reactive ion etching of a silicon dioxide mask layer on the surface of said substrate through a patterned photoresist material. 
     
     
       4. The process of claim 3, wherein the step of transferring the pattern of said etch mask to said substrate includes reactive ion etching of said mask. 
     
     
       5. The process of claim 4, wherein the step of reactive ion etching said substrate to form said trenches includes Cl 2  BCl 3  reactive ion etching. 
     
     
       6. The process of claim 5, wherein the step of undercutting and releasing said defined structure includes SF 6  /O 2  reactive ion etching. 
     
     
       7. The process of claim 6, wherein the step of depositing a conformal layer of metal includes sputter deposition of aluminum.